The present invention relates to a method for controlling a cruise control in a vehicle. The invention also relates to a vehicle cruise control system intended for such method for controlling said cruise control.
The present invention also relates to a computer program, computer program product and a storage medium for a computer all to be used with a computer for executing said method.
Motor vehicles, such as cars, lorries, towing vehicles and buses, are often provided with a so-called cruise control system, also denominated speed control system, for automatically controlling the vehicle speed. Such a cruise control system comprises means, such as a speed sensor, for monitoring the actual vehicle speed. The cruise control system compares the actual vehicle speed with a set target speed. The target speed may for instance be entered into the cruise control system as the prevailing actual vehicle speed when a set switch is actuated by the driver. The cruise control system generates an error signal by comparing the actual vehicle speed with the target speed. The error signal is then for instance used to control an actuator coupled to the fuel pump or to the vehicle throttle in order to change the engine speed until the error signal is substantially zero, i.e. until the actual vehicle speed is equal to the target speed.
EP1439976 and U.S. Pat. No. 6,990,401 disclose two examples of prior art where the cruise control system has been further developed. Here the cruise control system is a predictive cruise control system utilizing information about current vehicle position and upcoming road topography, that is for example gradients or elevation values for the coming road, in order to control throttle opening in such a way as to increase fuel efficiency.
It is desirable to further develop such a cruise control system where information about current vehicle position and upcoming road topography is used by the cruise control for controlling vehicle speed.
The method according to an aspect of the invention is a method for controlling a cruise control during driving of a vehicle. Said method comprising the steps of:                driving said vehicle with said cruise control active and set to maintain a vehicle set target speed;        registering a first vehicle position when driving in an uphill slope of a hill where vehicle retardation has decreased vehicle speed to a first vehicle speed below said vehicle set target speed and where said retardation has decreased to zero or the vehicle has just started to accelerate in order to increase vehicle speed to said vehicle set target speed;        registering a desired vehicle speed in a second position downhill of said crest at a first distance after said crest;        based on said desired vehicle speed calculating a minimum vehicle speed at said crest with which said vehicle has to pass said crest in order to be able to reach said desired vehicle speed with a minimized or zero fuel consumption during said first distance;        controlling vehicle speed during a second distance between said first vehicle position and said crest so that said vehicle reaches said minimum vehicle speed when passing said crest, and where a vehicle speed is maintained below said vehicle set target speed during said second distance.        
According to a first alternative embodiment of said invention said second vehicle position is one of;                a predetermined vehicle traveling time from said crest,        a predetermined distance from said crest,        at the end of said downhill,        at a distance from said crest where a vehicle traveling resistance is estimated to change from negative to positive.        
According to a further embodiment of said invention said method is characterized in further comprising the step of calculating a needed vehicle acceleration or retardation during said second distance in order to reach said minimum vehicle speed at said crest with a minimized fuel consumption during said second distance.
According to another embodiment of said invention said method is characterized in further comprising the steps of:                registering said first vehicle speed being just below a direct gear engagement vehicle speed;        when having registered a predetermined vehicle condition setting said minimum vehicle speed to equal said direct gear engagement vehicle speed and accelerating the vehicle up to said minimum vehicle speed and engaging a direct gear;        driving said vehicle with said direct gear engaged during remaining of said second distance.        
According to a further embodiment of the invention said predetermined vehicle condition comprises at least one of:                said just below a direct gear engagement vehicle speed meaning a speed difference below 5 km/h between said direct gear engagement vehicle speed and said first vehicle speed;        said second distance is greater than a predetermined value;        an estimated time interval for driving said vehicle with said direct gear engaged during said second distance is greater than a predetermined value.        
In another embodiment of the invention a maximum vehicle over speed is set for said vehicle cruise control, and where said maximum vehicle over speed is at least equal to or higher than said vehicle set target speed, and where said desired vehicle speed equals said maximum vehicle over speed.
According to another embodiment of the invention a minimum vehicle under speed is set, having a predetermined relation to said vehicle set target speed. According to a further embodiment said predetermined relation is one of:                said minimum vehicle under speed is a predetermined percentage of said vehicle set target speed;        said minimum vehicle under speed is a predetermined amount below said vehicle set target speed.        
In a further embodiment of the invention said crest, said second position and said minimum vehicle speed are predicted with information about present vehicle position and coming road topography of said hill.
According to a further embodiment of the invention if said second distance is shorter than a predetermined value, then said minimum vehicle speed is set to be equal to said first vehicle speed.
The invention also relates to a vehicle cruise control system that comprises (includes, but is not necessarily limited to) a control unit, driver input interface, vehicle position identifying device, road topography identifying device. Said system is characterized in that said control unit is arranged to perform the above mentioned method steps and use information from said vehicle position identifying device and said road topography identifying device in order to calculate said minimum vehicle speed.
Further advantageous embodiments of the invention emerge from the dependent patent claims following patent claim 1.